It happened at a shop on Cliftonville Road, Belfast last night, Monday, September 30.
At approximately 7.25 pm a man entered the shop and took an item from the chill cabinet.
When he approached the counter to pay for it he pointed what the member of staff believes was a gun and demanded money from the till.
He made off on foot with a sum of money.
The female member of staff was not injured during this incident, however she has been left very badly shaken by her ordeal.
The suspect is described as being in his early 20’s, thin build and wearing a black ‘rain’ jacket, dark grey tracksuit bottoms and light grey Nike trainers.
His face was covered with a black scarf.
Detective Sergeant O’Flaherty said: “I would appeal to anyone who saw this man in the area, or anyone who has information that they believe could help us with our investigation, to contact detectives at Musgrave on the non-emergency number 101, quoting reference 1820 30/09/19.
“Alternatively, information can also be provided to the independent charity Crimestoppers on 0800 555 111, which is 100% anonymous and gives people the power to speak up and stop crime.”